Curvic coupling fatigue life enhancement through unique compound root fillet design

A toothed coupling mechanism for maintaining assembly of rotating elements to a shaft in engines having hoop stressed components, said toothed coupling mechanism comprising:

• a curvic coupling having at least one male curvic coupling tooth and at least one female curvic coupling tooth, wherein said at least one male curvic coupling tooth matches said at least one female curvic coupling tooth, wherein said at least one male curvic coupling tooth has a first pressure surface and said at least one female curvic coupling tooth has a second pressure surface, wherein said at least one female curvic coupling tooth has a root, and wherein said at least one female curvic coupling tooth has a compound fillet formed between said second pressure surface and said root, wherein said compound fillet has a major fillet with a larger radius and a minor fillet with a smaller radius, said major fillet of said compound fillet is positioned in the root area of said at least one female curvic coupling tooth, and said minor fillet of said compound fillet connects the major fillet and the second pressure surface of said at least one female curvic coupling tooth, wherein background hoop stresses act on the major fillet resulting in 10% to 30% lower normalized stress concentration factor, wherein said larger radius and said smaller radius are optimized using finite element analysis, and wherein said compound fillet minimizes a penetration of a fillet surface of said at least one female curvic coupling tooth toward said at least one male curvic coupling tooth that matches said at least one female curvic coupling tooth, thereby providing an air flow gap, wherein when said coupling mechanism is coupled, the air flow gap includes a clearance formed between the tangency point of the minor fillet with the second pressure surface and a tip surface of the male curvic coupling tooth.

A gas turbine engine comprising a toothed coupling mechanism for maintaining assembly of a plurality of rotating elements to a shaft and transmitting torque between at least two rotating elements of said plurality of rotating elements in said gas turbine engine, wherein said toothed coupling mechanism comprises:

• a curvic coupling having at least one male curvic coupling tooth and at least one female curvic coupling tooth, wherein said at least one male curvic coupling tooth matches said at least one female curvic coupling tooth, wherein said at least one male curvic coupling tooth has a first pressure surface and said at least one female curvic coupling tooth has a second pressure surface, wherein said at least one female curvic coupling tooth has a root, wherein said at least one male curvic coupling tooth has a concave tooth profile and said at least one female curvic coupling tooth has a convex tooth profile, whereby a centering action is provided for maintaining assembly of the rotating elements to the shaft, and wherein said at least one female curvic coupling tooth has a compound fillet formed between said second pressure surface and said root, wherein said compound fillet has a major fillet with a larger radius and a minor fillet with a smaller radius, a ratio of said larger radius to said smaller radius being greater than 1.0, wherein said major fillet of said compound fillet is positioned in the root area of said at least one female curvic coupling tooth, and wherein said minor fillet of said compound fillet connects the major fillet and the second pressure surface of said at least one female curvic coupling tooth, wherein background hoop stresses act on the major fillet resulting in 10% to 30% lower normalized stress concentration factor, wherein said larger radius and said smaller radius are optimized using finite element analysis, and when said curvic coupling is coupled, said compound fillet allows a cooling air gap, the cooling gap includes a clearance formed between the tangency point of the minor fillet with the second pressure surface and a tip surface of the male curvic coupling tooth.

A coupling mechanism, comprising:

• a first toothed coupling member;
• a second toothed coupling member;
• said first and second toothed coupling members each having male teeth and female teeth, said male teeth of said first toothed coupling member mating with said female teeth of said second toothed coupling member, and, said female teeth of said first toothed coupling member mating with said male teeth of said second toothed coupling member;
• said female teeth having side portions and a root portion therebetween, said side portions being a side portion of the adjoining male teeth, said root portion forming a gable bottom;
• a compound fillet radius formed between said root portion and each of said side portions, said compound fillet radius having a first radius and a second radius, said first radius being greater than said second radius;
• said first radius beginning at a tangency point of the first radius with said root portion;
• said second radius beginning at a tangency point of the second radius with said side portion;
• said first radius and said second radius being meeting to form said compound fillet radius;
• and
• an air flow gap formed when said first toothed coupling member is mated with said second toothed coupling member, said air flow gap includes a clearance formed between the tangency point of the second radius with the side portion and a tip surface of the male curvic coupling tooth.